Methods for properly adjusting gibs on a cnc converted manual machine?

[mike96]

As the title asks, what methods are we using to properly adjust gibs? Obviously on a manual machine it would be tightened up and the table (or head/knee) moved untill you feel the axis you are adjusting tighten up then back off the gib a smidgen. With cnc however there is no "feel" feedback. My thought is to turn the peak amp output on the stepper control to approximately 1/3 of the normal peak amp out put, then tightening the gib while moving the axis until the stepper starts to stall out. Then back off the gib adjustment 1/8 - 1/4 turn and turn the stepper control back up.

What other methods are being used to adjust your gibs? Curious to know.

Mike.

 

[RJSakowski]

Here is what I do. I disconnect the stepper motor from the ball screw. Then I back the gib off. I measure the torque required to rotate the lead screw. I tighten the gib slightly and remeasure the torque. I repeat until I see the torque begin to rise and back the gib adjustment off slightly.

Tormach recommends a similar method where they back the gib off and measure backlash. They tighten the gib slightly and remeasure. They continue this until they see an increase in backlash which they attribute to lose motion due to increased resistance and they back the gib adjustment off slightly.

However, I have added checking for vertical and horizontal movement of the table when I apply reasonable force as a final sanity check.

 

[mike96]

Just curious. What are you using to measure torque with? I can see where adjusting the table with this method makes sense. Measuring backlash on the head makes the most sense, trying to measure torque on a 100+ pound head might be tough.

Mike.

 

[Huub Buis]

I adjust the gibs every time I startup the machines. My gib screws aren't locked. One by one, I release a screws and tighten them very very lightly with the tips of my fingers. It only takes a few seconds to do so and it is done before the machine is ready homing. I still can (and do) use the machines manually, so checking the gibs is easy.

 

[mike96]

I tried the method I outlined at the beginning of the thread and got not quite so good results, So I resorted to adjusting the Z By hand. I unmounted the head from the slide/carriage/saddle/whatever its called (Precision Matthews calls it a saddle), and the stepper. I then treated the ball screw like an old rotary phone. I put a slight bit of pressure on the saddle and rotated the ball screw with my hand to move the saddle up then let go of the screw. If the saddle moved back down a under light pressure, I adjusted the gib until it didn't. It dawned on me while adjusting the gib this way that I was going the wrong way with the adjustment screws and was loosening the gibs while doing the adjustment using the first method . So I figure this is a good starting point. Once it is back together I will test my theory again under power.